1. Field of the Invention
The present invention relates, in general, to a method and an apparatus for blow molding large hollow bodies, and more particularly, to a method and an apparatus for blow molding fuel tanks of a motor vehicle and the like.
2. Description of the Prior Art
In order to clarify the task of the present invention, one conventional method and apparatus for blow molding fuel tanks of a motor vehicle will be described with reference to FIGS. 6, 7A and 7B of the accompanying drawings
Referring to FIG. 6, there is shown but schematically a blow molding apparatus. Designated by numerals 1A and 1B are mold halves, each having a cavity formed therein, which are arranged for movement toward and away from each other. When the split mold halves 1A and 1B are coupled together, the cavities of them will define the walls of a product, viz., the blow-molded fuel tank. Positioned above the mold halves 1A and 1B is an injection head 2 from which a fluidized plastic material is fed into the cavity of the coupled mold halves. The injection head 2 is arranged to move vertically and connected to a known plastic material fluidizing machine (not shown). The injection head 2 delivers therefrom a tubular parison "P" of the fluidized plastic material. Designated by numeral 3 is an air nozzle from which compressed air is fed into the parison "P" to expand the same into engagement with the walls of the closed cavity of the coupled mold halves, as will become apparent hereinafter.
Referring to FIGS. 7A and 7B, there is shown a conventional mold carrier 10 which is incorporated with the vertically movable injection head 2. The mold carrier is movable rightwardly and leftwardly as indicated by the arrow "A" and carries thereon two sets of split molds 11 and 12, each split mold 11 or 12 including mold halves 1A and 1B. As shown, each mold half 1A or 1B is secured to a platen 14 of a hydraulic press device 13. Two air nozzles 3 are connected to the carrier 10, which are incorporated with the split molds 11 and 12, respectively.
In order to produce the fuel tank by using the above-mentioned blow molding apparatus, the following operation steps have been employed.
First, the mold carrier 10 is moved to one work position wherein one (for example, the mold 11) of the split molds 11 and 12 is positioned just below the injection head 2, as shown in FIG. 7A. Then, with the mold halves 1A and 1B kept separated, the injection head 2 delivers a parison "P" of the fluidized plastic material between the separated mold halves 1A and 1B. Then, by operating the hydraulic press devices 13, the mold halves 1A and 1B are moved toward each other and coupled together to pinch the parison "P". Then, compressed air is fed from the air nozzle 3 into the parison "P" to expand the parison "P" until the time when the wall of the parison "P" is tightly pressed against the walls of the closed cavity of the coupled mold halves 1A and 1B.
Thereafter, the mold carrier 10 is moved back to the other work position wherein the other (viz., the split mold 12) of the split molds 11 and 12 is positioned just below the injection head 2. Then, substantially same operation steps as the above-mentioned steps are carried out on the other split mold 12. During the molding steps on the mold 12, the previously finished mold 11 is cooled and then a product, viz., a molded fuel tank is removed from the mold 11 by separating the mold halves 1A and 1B.
However, the above-mentioned conventional blow molding method and apparatus have the following drawbacks.
First, due to the inherent construction of the mold carrier 10, four heavy and bulky hydraulic press devices 13 must be mounted on the mold carrier 10 for actuating the two split molds 11 and 12. This causes increase in weight and size of the mold carrier 10.
Second, because of the construction of the mold carrier on which only two split molds 11 and 12 are mounted, there is a severe limitation in speeding up the production cycle possessed by the apparatus.
Third, it is almost impossible to produce various types of products by using the apparatus. That is, in such case, various molds must be mounted to and removed from the mold carrier 10 one after another imposing a troublesome manual labor upon an operator.